Existing evidence, such as “National Diabetes Fact Sheet” by American Diabetes Association, indicates that currently approximately 18.2 million people in the U.S. have diabetes; and diabetes is the sixth-leading cause of death in the U.S. One in three Americans born in the year 2000 will develop Type 2 diabetes. With the large number of diabetes patients, and with the incidence of diabetes expected to increase, there is a continuously growing need for accurate glucose monitoring systems to monitor glucose levels. Continuous glucose sensors are designed to provide not only real-time glucose levels at a single point in time, but also the trend of a person's glucose levels based on analysis taking place every certain period of time with minimal finger-sticks, leading to improved glycemic/diabetes control.
Most contemporary continuous glucose sensors (hereafter CGS), however, yield blood glucose (hereafter BG) estimates by sampling interstitial glucose (hereafter IG) in interstitial fluid, rather than BG due to the difficulty in directly measuring BG in artery or blood vessels. A typical glucose (BG) estimation from IG is produced from at least two consecutive approximation steps: 1) Blood-to-interstitial glucose (BG-to-IG) transport; and 2) Derivation of BG values from IG-related electrical current recorded by the sensor. As a result, although CGS technology has made dramatic strides, the development of accurate and reliable CGS devices continues to face numerous challenges in terms of calibration, sensitivity, stability, and physiological time lag between blood and interstitial glucose concentrations. The difference between BG and CGS readings arises from following major factors: physiology, sensor calibration, noise, and engineering. The physiological time lag and gradients are changing dynamically with time, with BG levels, and across subjects; and the direct frequent in vivo sampling of IG is extremely difficult. Consequently, the evaluation of engineering performance of CGS is left with a central problem: separating the portion of BG/CGS error due to calibration, sensor noise, and BG/IG gradient.
Therefore, a method and apparatus are desired for improving accuracy and reliability of CGS.